Previously, Design Management would only serve the full size designs
that were uploaded, even when viewed as thumbnails.

https://gitlab.com/gitlab-org/gitlab/-/merge_requests/22860
introduced a change in the app to begin resizing designs down to a new
"v432x230" version.

This change refactors the existing Projects::DesignsController into a
new base class DesignManagement::DesignsController. The old controller
that served the full-size original design files is now
DesignManagement::Designs::RawImageController, and there is an
additional DesignManagement::Designs::ResizedImageController that can
serve resized versions of the designs.

This change represents a breaking change to the routes - however these
routes were only ever used internally. The extenal-facing parts of the
application (the GraphQL `DesignType`) has been updated with the new
routes.

https://gitlab.com/gitlab-org/gitlab/issues/12577
https://gitlab.com/gitlab-org/gitlab/issues/13815